Subject: Re: [Bug-wget] Anyone want to add libcares support to wget?

Re: [Bug-wget] Anyone want to add libcares support to wget?

From: Ben Greear <>
Date: Wed, 16 Mar 2016 07:35:44 -0700

On 03/15/2016 06:40 PM, Ángel González wrote:
> On 15/03/16 17:03, Ben Greear wrote:
>> I want to use wget on multi-homed machines, and I use routing rules to route pkts
>> out specific interfaces based on the source IP.
>> So, I need to be able to bind to a local IP address, including for the resolver logic,
>> which is why I want to use libcares.
>> To test, I think it would be sufficient to put two IPs on a port (,, and then
>> use cmd-line args to choose one or the other. Sniff and watch for proper source address.
>> For DNS servers, have and be specified. Sniff and watch to see that the
>> resolver destination IP is as specified. This should be completely independent of whatever
>> is in /etc/resolv.conf, etc.
>> I (and others) have patched libcares and curl in the past to handle all of this,
>> so I know libcares can do it. I think the main work is to handle new cmd-line
>> arguments, pass appropriate info to libcares, and make wget use libcares for it's
>> resolve logic.
>> Thanks,
>> Ben
> I think it's ok to add a --bind parameter to wget to choose the interface for download, but I don't think it should use a different resolver just for this.
> You _could_ change the libc nameservers from the application by changing _res.nsaddr_list after res_init(). It may be a bit fragile, but should work fine. And even better than changing each application, I would recommend you to create a simple LD_PRELOAD library that overrides res_init() & friends, and allows you to specify the target dns server with an environment variable. It's a pity there's no RESOLV_CONF var similar to RESOLV_HOST_CONF, for using a separate /etc/resolv.conf.

wget can already bind to a local IP. It might be nice to add support for SO_BINDTODEVICE, but not sure
it is required for what I need.

The rest of your suggestions are total hacks!

Anyway, I'm quite sure of what I want, and it should not be horribly difficult
to accomplish. I'll work on it if no one else is interested.


Ben Greear <>
Candela Technologies Inc
Received on 2016-03-16